Memcached magic

1. Memcached magic Ligaya Turmelle

2. What is memcached briefly? • memcached is a high-performance, distributed memory object caching system, generic in nature • AKA it is a key-based cache daemon that stores data and objects wherever dedicated or spare RAM is available for very quick access • It is a dumb distributed hash table. It doesn’t provide redundancy, failover or authentication. If needed the client has to handle that.

3. Why was memcached made? • It was originally developed by Danga Interactive to enhance the speed of LiveJournal.com • It dropped the database load to almost nothing, yielding faster page load times for users, better resource utilization, and faster access to the databases on a memcache miss • http://www.danga.com/memcached/

4. Where does memcached reside? • Memcache is not part of the database but sits outside it on the server(s). • Over a pool of servers

5. Pretty picture

6. When should I use memcached? • When your database is optimized to the hilt and you still need more out of it. • Lots of SELECTs are using resources that could be better used elsewhere in the DB. • Locking issues keep coming up • When table listings in the query cache are torn down so often it becomes useless • To get maximum “scale out” of minimum hardware

7. Use cases • anything what is more expensive to fetch from elsewhere, and has sufficient hitrate, can be placed in memcached • How often will object or data be used? • How expensive is it to generate the data? • What is the expected hitrate? • Will the application invalidate the data itself, or will TTL be used? • How much development work has to be done to embed it?

8. Why use memcached? • To reduce the load on the database by caching data BEFORE it hits the database • Can be used for more then just holding database results (objects) and improve the entire application response time • Feel the need for speed • Memcache is in RAM - much faster then hitting the disk or the database

9. Why not use memcached? • Memcache is held in RAM. This is a finite resource. • Adding complexity to a system just for complexities sake is a waste. If the system can respond within the requirements without it - leave it alone

10. What are the limits of memcached? • Keys can be no more then 250 characters • Stored data can not exceed 1M (largest typical slab size) • There are generally no limits to the number of nodes running memcache • There are generally no limits the the amount of RAM used by memcache over all nodes • 32 bit machines do have a limit of 4GB though

11. How do I easily install memcached? • You can build and install memcached from the source code directly, or you can use an existing operating system package or installation. • on a RedHat, Fedora or CentOS host, use yum: • root-shell> yum install memcached • on a Debian or Ubuntu host, use apt-get: • root-shell> apt-get install memcached • on a Gentoo host, use emerge: • root-shell> emerge install memcached • on OpenSolaris, use the pkg for SUNWmemcached: • root-shell> pkg install SUNWmemcached

12. How do I compile memcached from source? • Get the source from the website: http://www.danga.com/memcached/download.bml • Memcache has a dependancy on libevent so make sure you have that also. • Decompress, cd into the dir • ./configure;make;make install;

13. How do I start memcached? • Memcached can be run as a non-root user if it will not be on a restricted port (<1024) - though the user can not have a memory limit restriction • shell> memcached • Default configuration - Memory: 64MB, all network interfaces, port:11211, max simultaneous connections: 1024

14. Memcached options • You can change the default configuration with various options. • -u <user> : run as user if started as root • -m <num> : maximum <num> MB memory to use for items • If more then available RAM - will use swap • Don’t forget 4G limit on 32 bit machines • -d : Run as a daemon • -l <ip_addr> : Listen on <ip_addr>; default to INDRR_ANY • -p <num> : port

15. Memcached options (con’t) • -s <file> : unix socket (disables network support) • -c <num> : max simultaneous connections • -v : verbose • -vv : (2 v’s) very verbose • -P <file> : PID file (used with -d) • -t <threads> : number of threads to use to process incoming requests. Only valid if compiled with thread support enabled. Only useful up to number of CPU’s • There is a man page available with the install with a full listing of options.

16. How can I connect to memcached? • Memcached uses a protocol that many languages implement with an API. • Languages that implement it: • Perl, PHP, Python, Ruby, Java, C#, C, Lua, Postgres, MySQL, Chicken Scheme • And yes - because it is a protocol you can even use telnet • shell> telnet localhost 11211

17. Memcached protocol • 3 types of commands • Storage - ask the server to store some data identified by a key • set, add, replace, append, prepend and cas • Retrieval - ask the server to retrieve data corresponding to a set of keys • get, gets

18. Memcached protocol (con’t) • All others that don’t involve unstructured data • Deletion:delete • Increment/Decrement: incr, decr • Statistics: stats, • flush_all: always succeeds, invalidate all existing items immediately (by default) or after the expiration specified. • version, verbosity, quit

19. PHP and Memcached • Make sure you have a working Apache/PHP install • PHP has a memcached extension available through pecl. • Installation: • shell> pecl install memcache • Make sure the pear is installed (debian: apt-get install php-pear) • Make sure that you also have php5-dev installed for phpize. • shell> apt-get install php5-dev

20. PHP Script • Information about the PHP API at http://www.php.net/memcache <?php // make a memcache object $memcache = new Memcache; // connect to memcache $memcache->connect('localhost', 11211) or die ("Could not connect"); //get the memcache version $version = $memcache->getVersion(); echo "Server's version: ".$version."<br/>\n";

21. PHP Script (con’t) // test data $tmp_object = new stdClass; $tmp_object->str_attr = 'test'; $tmp_object->int_attr = 123; // set the test data in memcache $memcache->set('key', $tmp_object, false, 10) or die ("Failed to save data at the server"); echo "Store data in the cache (data will expire in 10 seconds)<br/>\n"; // get the data $get_result = $memcache->get('key'); echo "Data from the cache:<br/>\n"; echo ‘<pre>’, var_dump($get_result), ‘</pre>’;

22. PHP Script (con’t) // modify the data $tmp_object->str_attr = ‘boo’; $memcache->replace(‘key’, $tmp_object, false, 10) or die(“Failed to save new data to the server<br/>\n”); Echo “Stored data in the cache changed<br/>\n”; // get the new data $get_result = $memcache->get(‘key’); Echo “New data from the cache:<br/>\n”; Echo ‘<pre>’, var_dump($get_result), “</pre>\n”; // delete the data $memcache->delete(‘key’) or die(“Data not deleted<br/>\n”);

23. MySQL’s memcached UDF’s • Found at http://tangent.org/586/Memcached_Functions_for_MySQL.html • Will have to compile and build the functions • ./configure; make; make install; • May wish to copy the MySQL memcached UDFs into your MySQL plugins directory

24. MySQL’s memcached UDF’s (con’t) • you must initialize all the functions that you wish to have accessable within MySQL using CREATE and specifying the return value and library. (retained after restarts) • Ex: mysql> CREATE FUNCTION memc_get RETURNS STRING SONAME "libmemcached_functions_mysql.so"; • There is an SQL script in the UDF package to do this if you wish. • shell> mysql < sql/install_functions.sql

25. MySQL’s memcached UDF’s (con’t) • The API is consistent with the other API’s • Connect: mysql> SELECT memc_servers_set('192.168.0.1:11211,192.168.0.2:11211'); • The list of servers used by the memcached UDFs is not persistent over restarts of the MySQL server. • Set: mysql> SELECT memc_set('myid', 'myvalue'); • Retreive: mysql> SELECT memc_get('myid');

26. Possible ways to secure memcached • It has no authentication system - so protection is important • Run as a non-priveledged user to minimize potential damage • Specify the ip address to listen on using -l • 127.0.0.1, 192.168.0.1, specific ip address • Use a non-standard port • Use a firewall

27. Memcache project • Project home: http://code.google.com/p/memcached/ • Bug reports: http://code.google.com/p/memcached/issues/list • Internal MySQL see - https://steam.mysql.com/SOP:Memcached#Bugs

28. Memcached project (con’t) • SVN Source code: • Browse at http://code.google.com/p/memcached/source/browse/ • Use this command to anonymously check out the latest project source code: svn checkout http://memcached.googlecode.com/svn/trunk/ memcached-read-only • Non-members may check out a read-only working copy anonymously over HTTP.

29. Questions?